Pain is typically experienced when the free nerve endings of pain receptors are subject to mechanical, thermal, chemical or other noxious stimuli. These pain receptors can transmit signals along afferent neurons to the central nervous system and then to the brain. When a person feels pain, any one or more of a number of problems can be associated with this sensation, including but not limited to reduced function, reduced mobility, complication of sleep patterns, and decreased quality of life.
One known type of pain is radicular pain, which refers to pain that radiates along the dermatome of a nerve. This pain may be due to inflammation or other irritation of the nerve root at its connection to the spinal column. A common form of radiculitis is sciatica, or radicular pain that radiates along the sciatic nerve from the lower spine to the lower back, gluteal muscles, back of the upper thigh, calf, and foot as often secondary to nerve root irritation from a spinal disc herniation or from bone spurs or ostophytes in the lumbar region of the spine.
The causes of pain include but are not limited to inflammation, injury, disease, muscle stress, the onset of a neuropathic event or syndrome, and damage that can result from surgery or an adverse physical, chemical or thermal event or from infection by a biologic agent. When a tissue is damaged, a host of endogenous pain inducing substances, for example, bradykinin and histamine can be released from the injured tissue. The pain inducing substances can bind to receptors on the sensory nerve terminals and thereby initiate afferent pain signals. After activation of the primary sensory afferent neurons, the projection neurons may be activated. These neurons carry the signal via the spinothalamic tract to higher parts of the central nervous system.
One known class of pharmaceuticals to treat pain is opioids. This class of compounds is well-recognized as being among the most effective type of drugs for controlling pain, such as post-operative pain. Unfortunately, because opioids are administered systemically, the associated side effects raise significant concerns, including disabling the patient, depressing the respiratory system, constipation, and psychoactive effects such as sedation and euphoria, thereby instituting a hurdle to recovery and regained mobility. Consequently, physicians typically limit the administration of opioids to within the first twenty-four hours post-surgery. Thus, it would be preferable to use non-narcotic drugs that deliver direct, localized pain control at a surgical site.
One pharmaceutical that is known to the medical profession is clonidine, which is widely recognized as an antihypertensive agent that acts as an agonist on the alpha-2-adrenergic receptor and as a neural receptor agonist. In general, clonidine, also referred to as 2,6-dichloro-N-2-imidazolidinyldenebenzenamine (C9H9Cl2N3) may be represented by the following chemical structure:

Another pharmaceutical that is known to the medical profession is bupivacaine, which is widely recognized as a local anesthetic for infiltration, nerve block, epidural and intrathecal administration. In general, bupivacaine, also referred to as 1-butyl-N-(2,6-dimethylphenyl) piperidine-2-carboxamide (C18H28N2O) may be represented by the following structure:

Another pharmaceutical that is known to the medical profession is lidocaine, which is widely recognized local anesthetic. Lidocaine is also a class Ib antiarrhythmic agent, blocking the sodium channel of the cardiac action potential, which reduces the slope of phase 0 of depolarization with little effect on the PR interval, QRS complex or QT interval.
There have been numerous proposals for which active ingredients are most effective for treating pain, including radicular pain. Because different active ingredients, and different vehicles for administering them have different benefits and risks, there is a need to develop better compositions and methods for administering active ingredients in different vehicles to treat pain at the same target site.